The Applicant has developed a range of Memjet® inkjet printers as described in, for example, WO2011/143700, WO2011/143699 and WO2009/089567, the contents of which are herein incorporated by reference. Memjet® printers employ a stationary pagewidth printhead in combination with a feed mechanism which feeds print media past the printhead in a single pass. Memjet® printers therefore provide much higher printing speeds than conventional scanning inkjet printers.
An inkjet printhead is comprised of a plurality (typically thousands) of individual inkjet nozzle devices, each supplied with ink. Each inkjet nozzle device typically comprises a nozzle chamber having a nozzle aperture and an actuator for ejecting ink through the nozzle aperture. The design space for inkjet nozzle devices is vast and a plethora of different nozzle devices have been described in the patent literature, including different types of actuators and different device configurations.
Most current inkjet printheads comprise one or more MEMS printhead integrated circuits, whereby inkjet nozzle devices are fabricated on a CMOS silicon wafer using MEMS fabrication techniques. Integration of MEMS and CMOS features is a crucial aspect of MEMS printhead design.
Research Disclosure 596074 and U.S. Pat. No. 6,938,340 describe inkjet nozzle devices comprising a MEMS layer disposed on a silicon-on-insulator substrate. The insulator layer facilitates control of backside ink channel etch processes.
Some types of inkjet nozzle devices employ an actuator bonded to the roof of a nozzle chamber. For example, U.S. Pat. No. 7,654,645 describes thermal bubble-forming actuators bonded to the roof of the nozzle chamber; U.S. Pat. No. 5,812,162 describes thermal actuators bonded to the roof of the nozzle chamber, which warm ink to reduce surface tension and cause droplet ejection; U.S. Pat. No. 7,819,503 describes nozzle chambers having a moving roof portion comprising a thermoelastic bend actuator; and U.S. Pat. No. 5,828,394 describes a nozzle chamber having a moving roof portion comprising piezoelectric actuator.
Roof-bonded actuators present different design challenges compared to more usual floor-bonded actuators. This is because MEMS-CMOS integration must deliver power efficiently from drive transistors in the CMOS layer up to the actuators in the MEMS layer, inevitably using electrical connectors which extend over a height of the nozzle chamber. This, in turn, places practical limitations on nozzle chamber heights.
U.S. Pat. No. 7,794,056 and U.S. Pat. No. 7,819,503 describe two different types of electrical connectors for delivering current to a thermoelastic actuator positioned in a moving portion of a nozzle chamber roof.
It would be desirable to provide a printhead have excellent nozzle plate robustness. It would further be desirable to provide an improved fabrication process for integrating MEMS and CMOS features. It would further be desirable to provide inkjet nozzle devices having roof actuators with excellent electrical efficiency and, particularly, power transfer from drive circuitry which is independent of nozzle chamber height.